For a discussion of the background of the invention reference may be made to Liang '700 cited above. Liang '700 discloses a method for manufacturing ACFs having a non-random array of conductive particles by providing a carrier web having a non-random array of microcavities and distributing the conductive particles into the microcavities. Preferably, the particles are distributed on the carrier web so that there is essentially one particle in each cavity. The carrier web is conveyed into contact with an adhesive film and the particles are transferred to the film upon contact.
One method that is used to form microcavities in the carrier web is laser ablation micromachining using for examples, KrF and ArF excimer lasers through a mask. See commonly assigned U.S. Publications 2009/0053859; 2010/0101700; and 2012/0295098 incorporated herein in their entireties by reference.
It has been reported that the local surface temperature of the polymer to be ablated can reach greater than 1000° K with a relatively high pressure ablation plume usually from few tens to few hundreds bars. Microstructure formation due to debris re-deposition and re-solidified lateral material melt flow from the center to the periphery of the laser irradiated spot have been observed. For fine pitch image reproduction particularly those of high aspect ratio (i.e., the height/width or depth/width ratio of an image or image spacing), the resolution achievable by such a process is often severely degraded by the undesirable light diffraction and scattering attributable to the mask used and the aforementioned material melt flow, debris formation and re-deposition induced by the photothermal process.
It has also been reported that improved aspect ratio and resolution can be achieved by using a projection mask with coherent image correction, multi-pulse irradiation of various wavelength on various substrates, filtered irradiation, liquid-assisted or under-water irradiation. However, in all cases, manufacturing of fine-pitch (about <15 um) images of narrow pitch spacing (about <5 um) and high aspect ratio (about >1) of image spacing remains a major challenge, particularly in a roll-to-roll process.